Mortar compositions in the form of dry powder ready for use have been known for a long time, comprising at least one powdery binder and at least one aggregate, as well as possibly at least one standard additive and/or adjuvant, and formed from particles, at least some of which, referred to as fine particles, are liable to produce an emission of dust. This type of composition, generally referred to as “industrial” mortar, is a mortar batched and mixed in the factory. It is “dry”, that is to say ready to be mixed with water.
Amongst the aforementioned binders, mineral binders can be cited, such as slaked lime, cements, gypsum render/plaster or the like, and organic binders, such as for example certain synthetic resins. As aggregates (sometimes referred to as agglomerates), sand, stone powder, crushed brick or the like can be mentioned.
The expression mortar means all compositions meeting the particularities given above and therefore also renders/plasters. “Render/plaster coat” means a layer applied in one or more passes using the same mortar, without leaving the first pass to dry before applying the second. Then the “undercoat” or sub-layer coat is distinguished, namely the “bottom layer or layers of a system”, of the “final coat” or façade coat or finishing coat; namely the “top layer of a multi-coat system”.
The aforementioned industrial mortars and ready dry renders/plasters have the well-known long-standing drawback of high emission of dust both during manufacture by mixing their constituent components, during bagging and during manipulation before mixing on the site of use.
This emission of dust is the subject of regulation on the protection of workers, which is continually being strengthened.
Moreover, the aforementioned emission of dust gives rise to a degradation of the local environment, in the factory and on the site, requiring particularly constraining cleaning and protection work. The problem of the emission of dust is particularly critical during work in a closed habitat, in particular during renovation of inhabited interiors.
Finally, the emission of dust will mainly concern the fractions of mortars and renders/plasters having the finest particles, which are often the low-content adjuvants. These constituents are in general the most critical and the most expensive in the formulation; if they partially get into the atmosphere in the factory and/or on the site this may lead to an imbalance in the composition of the mortar and therefore to a loss of performance.
In any other field, it is known how to reduce the emission of dust emitted during the treatment of soil with quicklime, by the agglomeration of the lime fines by means of a non-aqueous fluid additive [EP 0880569 B2].
The addition, to the mortars and renders/plasters, of polar organic liquids, in particular functionalised polyolefins having for example carboxylic functions or any other equivalent function (alcoholic or phenolic), is known so as to improve the adhesion and workability of the compositions, for the purpose of limiting the addition of water during mixing (reduction in the water/binder ratio) [JP 08081249, JP 05058695, U.S. Pat. No. 4,586,960]. It should however be noted that in no cases have such polar compounds been deemed to reduce the emission of dust from the compositions to which they have been added.
“Workability” means all the properties of use of a mortar that confer on its suitability for use. This concept is also sometimes referred to as “plasticity”.
Compositions are known for repairing cracks in walls (see WO 00/34200). According to circumstances, these compositions are before use in the form of a paste containing a large proportion of water or in a dry form to which water is added before application. In order, after hardening of the joints, to avoid the latter emitting dust in an undesirable manner during sanding, provision is made in the document for adding to the paste containing water or to the powder mixed with water a dust-suppressant liquid additive. As an alternative, a coating of the hardened joint with a layer of the dust-suppressant liquid additive is also provided.